| alt.engineering.electrical, firstname.lastname@example.org says...
|> | In article <37adfe4a-b085-4dd3-a291-
|> |> > I've searched all through my 2005 NEC looking for some guidance as to how
|> |> > many 12/2 circuits I can run through a single 3/4" hole in the wall
|> |> > a house I'm building as a retirement project. I can not find anything
|> |> > it. I've also asked on several over groups. Is there some rule of thumb
|> |> > is there an actual regulation that I'm missing. I'm way out in the
|> |> > and we do not have an inspector that I can ask and the one in the county
|> |> > seat said there is no restriction. I'm not concerned about county
|> |> > restrictions, I'm concerned about safety.
|> |> >
|> |> > TIA
|> |> >
|> |> > --
|> |> > JC from Gnat Flats
|> |> There are no rules on this in the 2005 NEC. As long as you keep the
|> |> cables separated and not bundled and do not apply fire stopping you
|> |> can put as many cables through a hole in a stud and will fit.
|> |> If you apply fire stopping you must derate according to the 2008 NEC.
|> | Doesn't that seem sorta silly?
|> No. A simple short (2 inches) hole does not tend to impact the ability
|> of the wires to carry heat away and dissipate it into air a few inches
|> away. OTOH, a fire stop would be more constraining on the wires and
|> could reduce the heat dissipation.
| Maybe I misunderstand incorrectly what a "fire stop" is here. I
| thought it was stuff to plug the holes so no air could move through
| the hole in the 2x. With the hole filled, the center of the wire
| is still only 3/4" from free air on either side of the 2x.
Without the fire stop, the ability to dissipate is my multiple means.
It can dissipate _some_
within the hole, and _some_
through the wires
to the free air away from the hole. The fire stop would have the
effect of reducing or eliminating _one_
of these means of heat escape.
That is, afterall, its design purpose.
| It seems silly to derate the wire, since that means more holes in
| the fire stop.
More holes would be if you reduce the bundling rate to _avoid_
or as much derating. Otherwise it means using _larger_
wire that is
treated as rated less. The latter might have to be the way to do it if
the number of holes is an issue (as building construction code or safe
engineering may dictate).
I think the derating could be more flexible, such as a variant rating
factor for the length of the run, and the heat transfer capability of
the containing material. But this can also get complex and would need
to be one of those "under engineering supervision" things (where a PE
puts his license on the line).
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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